This invention relates generally to drip irrigation tape and to methods and apparatus for fabricating such tape.
The drip irrigation system consists of lengths of plastic tubing or tape placed above ground or underground near the roots of plants, the tubing having numerous small outlets supplying drops of water continuously to the plants. This allows the amount of water supplied to be controlled more precisely, conserving water, improving crops and reducing salt accumulation and fertilizer loss in the soil.
In my previous U.S. Pat. Nos. 4,722,759 and 4,807,668, referred to above, a drip irrigation tape is described in which a strip of flexible material is formed with an indented groove extending lengthwise adjacent one side edge of the strip, the other side edge being folded over to overlap the first side edge and form a first or main water conduit. The overlapping side edges are sealed together on opposite sides of the groove to form a seam in which the groove defines a secondary conduit. Spaced inlets from the first conduit to the secondary conduit and outlets from the secondary conduit are provided, so that fluid supplied to the first conduit flows into the secondary conduit and from there leaks slowly out of the outlets into the surrounding soil.
A method and apparatus for fabricating such tape was described in my previous patents, which consisted of first forming the groove on a vacuum drum, then folding the strip lengthwise before sealing the overlapping edges at or close to the opposite sides of the groove by means of a heat sealing wheel.
In my previous patents the secondary conduit was formed by a straight, continuous or segmented channel. However, there is some advantage in providing a non-straight path to create some turbulence in the fluid flowing along the channel or conduit. Thus, in U.S. Pat. No. 4,473,191 of Chapin one of the embodiments shows a drip irrigation tape in which the flow restricting passage is in the form of a zig-zag or serpentine path. In this case the passage is formed by depositing a flat ribbon of plastic onto one side edge of the tape and then deforming the ribbon to form the serpentine path using a suitable molding wheel. One problem with zig-zag flow restricting passages is that small particles of soil or dirt may become trapped in the confined space of the passage, blocking flow along the passage and thus reducing or stopping the flow of water into the soil.